Synchronisation of breeding in populations of the brown mussel Perna perna on the South Coast of South Africa
- Authors: Ndzipa, Victoria
- Date: 2013-05-28
- Subjects: Mussels -- South Africa , Perna -- South Africa , Perna -- Breeding
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5830 , http://hdl.handle.net/10962/d1007857 , Mussels -- South Africa , Perna -- South Africa , Perna -- Breeding
- Description: The general biology and seasonality of breeding of intertidal populations of the brown mussel Perna perna in South Africa are reasonably well known, but we have little information on variability either within or among populations. Synchronous spawning offers adaptive advantages to externally breeding animals. Firstly, it enhances fertilization rates and therefore the species' reproductive fitness. Secondly, spawning can also be timed to coincide with environmental conditions conducive to larval settlement and development. In addition, synchronisation of spawning will influence the synchrony of settlement. Synchronisation of larval settlement, in turn, has implications for popUlation biology, as highly pulsed settlement is likely to lead to density-dependant mortality of recruits and uncoupling of adult/recruit densities, while poorly synchronised settlement will not. Generally, sea temperature and food availability are considered the key factors underlying the initiation and the duration of the breeding cycle of mussels. However, there are proximate local cues that trigger the proliferation, maturation and release of gametes. In this study, the hypothesis tested is that factors that control food availability affect gonad development and so influence synchrony among populations. Much of the published work on spawning is based on observations of the presence of larvae in the plankton, or on settlement. A more reliable method correlates the sequence of gonad development throughout the year with changes in length-weight relationships, using histology. This study is also designed to investigate temporal differences in the timing of the breeding cycle between sheltered and exposed sites along the south coast of South Africa by histological analysis of the reproductive tissue (the gonad) and by dry weight/shell length regreSSIOns. To do this, these two techniques were applied to six mussel populations at three III ocalities that were separated on scales of about 10-20km. Within each locality, two study sites were .dentified. One was exposed to strong wave action and one was sheltered. A few hundred meters ;eparated these sites. The first technique used length-weight regressions as an indication of mussel ~ondition. Abrupt decreases in the dry body weight of a hypothetical standard animal were taken to indicate periods of spawning. Regressions were assessed for samples of 40 mussels taken from each site at intervals of 4 weeks over 13 months. The results were analysed using a 3-way ANCOV A, with dry weight as the dependent variable, shell length as a covariate, and site, exposure and month, as independent variables. The second approach used the more reliable and detailed method of assessing the annual reproductive cycle using histological sections of the gonad. Histological sections of gonads from thirty female mussels, sampled monthly from each site, were examined in the laboratory. Each gonad was categorized into one of six arbitrary developmental stages based on ovary morphology. Synchrony in spawning was examined by comparison of gonad developmental stages of individuals within and among populations. The data were analysed by 3-way nested ANOV A with mean gonad index for each population as the dependent variable, month as an independent variable and exposure nested in site. The results obtained from both techniques showed strong synchronisation among different popUlations, regardless of the scales at which they were separated. The data also indicated good synchrony within populations and, again among populations, regardless of the degree of exposure. The results also indicated that the gonad condition varied significantly at each site, exposure level and month. However, there were significant interactions among these three factors. This means that on a broader seasonal scale the six mussel populations were reasonably synchronised, but on finer monthly scales, there were temporal differences in duration of gametogenic events. The implication is that ovary development is cued by environmental factor(s) that operate on scales of at least 7-20 km rather than more localised events that may affect food availablity either through aggregation of food (local hydrography at different localities) or food delivery to the shore (degree of wave action at different sites.) , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
The effect of mussel bed structure on the associated infauna in South Africa and the interaction between mussel and epibiotic barnacles
- Authors: Jordaan, Tembisa Nomathamsanqa
- Date: 2011
- Subjects: Mytilidae -- South Africa , Mytilus galloprovincialis -- South Africa , Mussel culture -- South Africa , Shellfish culture -- South Africa , Perna -- South Africa , Barnacles -- South Africa , Mussels -- South Africa , Mussels -- Ecology , Barnacles -- Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5675 , http://hdl.handle.net/10962/d1005360 , Mytilidae -- South Africa , Mytilus galloprovincialis -- South Africa , Mussel culture -- South Africa , Shellfish culture -- South Africa , Perna -- South Africa , Barnacles -- South Africa , Mussels -- South Africa , Mussels -- Ecology , Barnacles -- Ecology
- Description: Mussels are important ecological engineers on intertidal rocks where they create habitat that contributes substantially to overall biodiversity. They provide secondary substratum for other free-living, infaunal or epifaunal organisms, and increase the surface area for settlement by densely packing together into complex multilayered beds. The introduction of the alien invasive mussel Mytilus galloprovincialis has extended the upper limit of mussels on the south coast of South Africa, potentially increasing habitat for associated fauna. The aim of this study was to describe the structure of mussel beds, the general biodiversity associated with multi- and monolayered mussel beds of indigenous Perna perna and alien M. galloprovincialis, and to determine the relationship between mussels and epibiotic barnacles. This was done to determine the community structure of associated macrofauna and the role of mussels as biological facilitators. Samples were collected in Plettenberg Bay, South Africa, where M. galloprovincialis dominates the high mussel zone and P. perna the low zone. Three 15 X 15 cm quadrats were scraped off the rock in the high and low zones, and in the mid zone where the two mussel species co-exist. The samples were collected on 3 occasions. In the laboratory mussel-size was measured and sediment trapped within the samples was separated through 75 μm, 1 mm and 5 mm mesh. The macrofauna was sorted from the 1 mm and 5 mm sieves and identified to species level where possible. The epibiotic relationship between mussels and barnacles was assessed by measuring the prevalence and intensity of barnacle infestation and the condition index of infested mussels. Multivariate analysis was used on the mean abundance data of the species for each treatment (Hierarchical clustering, multidimensional scaling, analysis of similarity and similarity of percentages) and ANOVA was used for most of the statistical analyses. Overall, the results showed that tidal height influences the species composition and abundance of associated fauna. While mussel bed layering influenced the accumulation of sediments; it had no significant effect on the associated fauna. Time of collection also had a strong effect. While there was an overlap of species among samples from January, May and March, the principal species contributing to similarity among the March samples were not found in the other two months. The outcomes of this study showed that low shore mussel beds not only supported a higher abundance and diversity of species, but were also the most structurally complex. Although the condition index of mussels did not correlate to the percentage cover of barnacle epibionts, it was also evident that low shore mussels had the highest prevalence. The levels of barnacle infestation (intensity) for each mussel species were highest where it was common and lowest where it was least abundant. This is viewed as a natural artefact of the distribution patterns of P. perna and M. galloprovincialis across the shore. Mussels are more efficient as facilitators on the low mussel zone than the high mussel zone possibly because they provide habitats that are more effective in protecting the associated macrofauna from the effects of competition and predation, than they are at eliminating the effects of physical stress on the high shore. Although mussels create less stressful habitats and protect organisms from the physical stress of the high shore, there are clear limitations in their ability to provide ideal habitats. The biological associations in an ecosystem can be made weak or strong depending on the external abiotic factors and the adaptability of the affected organisms.
- Full Text:
- Date Issued: 2011
The effects of the invasive mussel mytilus galloprovincialis and human exploitation on the indigenous mussel Perna perna on the South Coast of South Africa
- Authors: Rius Viladomiu, Marc
- Date: 2005
- Subjects: Mussels -- South Africa , Perna -- South Africa , Mytilus galloprovincialis -- South Africa , Mytilidae -- South Africa , Biological invasions , Marine resources conservation -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5684 , http://hdl.handle.net/10962/d1005370 , Mussels -- South Africa , Perna -- South Africa , Mytilus galloprovincialis -- South Africa , Mytilidae -- South Africa , Biological invasions , Marine resources conservation -- South Africa
- Description: In South Africa, the indigenous mussel Perna perna is threatened by both an invasive species and excessive human exploitation. The Mediterranean mussel Mytilus galloprovincialis is an invasive species that has been introduced to many parts of the world. In South Africa, this species arrived in the 1970s and spread rapidly along the west coast where today it is the dominant mussel species. Along the west coast, M. galloprovincialis is competitively superior in all aspects to the indigenous mussel species, and, as a result, has displaced some of them. On the south coast, M. galloprovincialis found more oligotrophic waters, higher species richness, and a stronger competitor in the indigenous mussel P. perna. The rate of spread of M. galloprovincialis along the south coast has decreased over the last 10 years and the present eastern limit of its distribution in South African is East London. On the south coast, M. galloprovincialis has not yet completely replaced P. perna; instead, the two exhibit spatial segregation, with P. perna dominating the low shore, M. galloprovincialis the high shore and an overlap zone between the two. An experiment on competition was carried out at one site on the south coast. The results showed that, on the low shore, P. perna is a more dominant competitor for space than M. galloprovincialis. Also byssus attachment of the two species differs, P. perna being much stronger than M. galloprovincialis, which suffers high mortality due to wave action on the low shore, especially in monospecific beds. As a result, mortality of M. galloprovincialis through wave action is reduced by the presence of P. perna, which seems to confer protection against dislodgement. However, in the absence of strong wave action, P. perna competitively excludes M. galloprovincialis. Human exploitation along 160 km of coast was examined by sampling mussel populations and using aerial surveys to determine where harvesters were distributed. Collectors did not seem to discriminate between species. The study has shown that higher abundances of mussels were found in protected or inaccessible sites, while in unprotected sites mussels were scarce. Coastal nature reserves are being proven to be effective in protecting mussel populations.
- Full Text:
- Date Issued: 2005
Effects of small-scale water movement on the settlement and growth rates of the brown mussel Perna perna, on the south-east coast of South Africa
- Authors: Mathagu, Tendamudzimu Titus
- Date: 2003
- Subjects: Mussels -- South Africa , Perna -- South Africa , Perna -- Growth
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5682 , http://hdl.handle.net/10962/d1005368 , Mussels -- South Africa , Perna -- South Africa , Perna -- Growth
- Description: The effects of small scale (cm) water movement on the settlement and growth rates of the brown mussel Perna perna were investigated on the south-east coast of South Africa (33°28′S, 27°10′E). L-shaped metal baffles attached to the substratum decreased the erosion rates of cement balls and it was concluded that the baffles decreased the water flow rate around cement balls. These L-shaped baffles were then used to decrease water flow rates around mussel patches and pot-scouring pads used as artificial substrata for the settlement of P.perna larvae. Anova indicated that settlement rate varied by date and site while decreased water flow rate significantly increased larval settlement (p<0.05), only on the site and day that had the overall highest number of settlers. Mussels in the low zone had significantly higher growth rates than those in the high zone. Decreased water flow rate significantly increased mussel growth rate in the lower zone (Anova, p<0.05), while it did not have a significant effect on the mussel in the high zone. Thus water flow manipulation increased growth rates in the zone, which already had high growth rate. It was concluded that small-scale (cm) water flow patterns have an effect on both Perna perna settlement and growth rates, but only under specific conditions. Larval settlement rate was significantly increased by water flow manipulation on the site and day that had the highest number of settlers. Growth rates were significantly increased by decreased water flow rate only in the low zone, where growth rates are the highest. Although water flow was manipulated in both zones its effect in the high zone was insignificant (Anova) compared to other factors affecting growth rates at this tidal level.
- Full Text:
- Date Issued: 2003
Effects of zone and wave exposure on population structure and recruitment of the mussel (Perna perna) in South Africa
- Authors: Lindsay, Justin Robert
- Date: 1999
- Subjects: Perna -- South Africa , Perna -- Growth , Mussels -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5685 , http://hdl.handle.net/10962/d1005371 , Perna -- South Africa , Perna -- Growth , Mussels -- South Africa
- Description:
Certain aspects of the population dynamics of the brown mussel, Perna perna, were examined at 18 sites along the south coast of South African. Specifically the effects of wave exposure and tidal height were examined in relation to mussel size, biomass and density. A single set of samples was removed from each of the 18 sites, over three spring tide cycles. Sites were classified as exposed or sheltered prior to sampling. Principal component analysis (PCA) (based on mussel length data) and length frequency histograms revealed that there was a general decrease in the modal size of the adult mussel cohort with an increase in tidal height. The effects of exposure on mussel size decreased higher on the shore. On the exposed low shore the maximum size of mussels had a mean length of 102.3mm and was significantly larger (ANOVA, p<0.0001) than that for mussels on sheltered shores (86.7mm). The difference between mean maximum lengths of mussels on the mid shore was not so great, exposed sites had a average mean maximum length of 79.9, while on the sheltered shores it was 68.4mm. On the high shore the difference between the average mean maximum lengths at exposed and sheltered sites was only 3.9mm. The fact that the effects of exposure were greatest on the low shore was also borne out in the PCA. In this analysis low shore exposed and sheltered zones separated into two groups with little overlap, mid shore exposed and sheltered zones were positioned next to each other, and exposed and sheltered high shore zones were clumped together. Densities of adult mussels (>l5mm) were calculated as real densities from randomly placed quads i.e. not from areas of 100% cover. Density decreased up the shore; low, mid and high shore zones were significantly different from each other (ANOVA , p<0.0001; followed by multiple range tests). There was no significant difference between the densities of mussels at exposed and sheltered sites within each zone (ANOVA, p=0.7155). Recruit (
- Full Text:
- Date Issued: 1999
Population dynamics and growth rates of the brown mussel (Perna perna) on wave exposed and wave sheltered shores of South Africa
- Authors: Lindsay, Tracy Lynn
- Date: 1999
- Subjects: Perna -- South Africa , Mussels -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5741 , http://hdl.handle.net/10962/d1005427 , Perna -- South Africa , Mussels -- South Africa
- Description:
Population dynamics of Perna perna in low shore mussel beds were investigated over a 15 month period at six sites along the south coast of South Africa, with particular reference to the effects of wave exposure. The degree of exposure was first quantitatively ascertained using the dissolution of cement blocks to measure average wave force and dynamometers to measure maximum wave force. The mean mass loss of the cement blocks was higher at Diaz Cross and Kwaai Hoek than at Mgwalana, Rufanes and Riet River. No data were available for Fish River. The mean maximum wave force encountered at Diaz Cross, Kwaai Hoek and Fish River was significantly higher (p
- Full Text:
- Date Issued: 1999